The short answer
American Standard error codes show up in three places: the touch-screen thermostat on the wall, the display or blinking light on the furnace, and the control board in the outdoor unit. In Northern Virginia winters, the alerts that bring the most calls are 126.00 (part of the system stopped communicating), 79 (the heat pump’s low pressure switch tripped) and 157.00 (the condensate float switch shut the system down). Write down the code and its color, check the breakers and the drain, power cycle once, and call if it returns.
Where American Standard codes show up
On the wall. American Standard’s touch-screen controls, the 824, 850 and 1050 and the newer Link thermostats, show numbered alerts from the whole system. They’re the same numbers Trane uses, because the two brands are built by the same company.
On the furnace. A code through the door window like E3.2, or a blinking red light. Those have their own guide: American Standard furnace error codes.
Outside. The control board in the heat pump or air conditioner. Variable-speed AccuComfort units send their codes to the thermostat; older units blink a light on the board.
The $67 Heating Check
We check your furnace, heat pump or boiler before winter. Through December 31. See the offer
Reading the alert on the thermostat
On the 824, 850 and 1050, open the Service Menu, then Diagnostics. Current Alerts shows what’s active and Alert History keeps 30 days; tap a code for its description. On a Link thermostat it’s Menu, then System Info, then Alerts. The manufacturer’s 850 control installation guide spells out the menus.
The color matters more than the number at first. A red alert means heating or cooling has stopped. Yellow means it’s running but limiting itself. Minor alerts only show in Diagnostics and don’t need a visit.
Heat pump iced over, with a 79 alert
A little frost in winter is normal; the heat pump melts it off in a defrost cycle every so often. A solid block of ice is not. When the coil ices up, refrigerant pressure drops, the low pressure switch opens, and the thermostat shows 79. After the third trip the outdoor unit holds a hard lockout until the power is cycled. Causes run from a stuck defrost board or a bad sensor to low refrigerant from a leak. Clear snow and leaves from around the unit and power cycle once, then read heat pump covered in ice. If it trips again, it needs a tech.
Running on aux heat all the time
When the heat pump can’t keep up or is locked out, the thermostat brings on the electric backup heat and shows Aux. That’s fine on the coldest mornings. All day, every day, it usually means the outdoor unit has stopped: a 79 lockout, a low refrigerant charge, or a defrost problem. Your electric bill will tell you before anything else does. Check the alerts, and see aux heat versus emergency heat for what each setting does. A 153 or 154 alert means the backup heat strips themselves overheated or aren’t getting enough air, which is usually a filter.
No heat or cooling and a red 126.00
A piece of equipment stopped talking to the thermostat. On these systems two of the thermostat wires carry data, so a loose wire, a tripped breaker on just the indoor or just the outdoor unit, a power surge or a failed board can all do it. After a new install, 91.05 or 91.06 alongside it points to a wiring mistake. Check both breakers and the disconnect by the outdoor unit, power cycle once, and call if it comes back. The 126.00 walk-through goes step by step.
System stopped and 157.00
The condensate float switch felt water backing up and shut everything off before it overflowed. Look in the pan under the indoor unit and at the condensate pump, if you have one. A full tank and a humming pump means the pump quit. Furnaces make water all winter, so this one isn’t only a summer code.
Outdoor unit stops and restarts
An 80 alert is the high pressure switch. In summer it’s usually a dirty outdoor coil or an outdoor fan that stopped; in winter it can be low airflow inside from a clogged filter. Change the filter and watch the outdoor fan. A 158 alert is the indoor coil freezing, again usually airflow or low refrigerant.
Common American Standard alert codes
Swipe to see all columns →
Swipe to see all columns →
| Code | What it means |
|---|---|
| 126.00 | A piece of equipment stopped communicating |
| 89.00 / 89.01 | Equipment the thermostat expects is missing |
| 91.00 / 91.01 | The blower or inducer stopped communicating |
| 91.02 | System communication error on the data wire |
| 91.03 | No system clock |
| 91.05 / 91.06 | Data wiring miswired or shorted, common right after an install |
| 90.x | Communication dropping in and out |
| 79.xx | Low pressure cutout on the outdoor unit; locks out on the third trip |
| 80.xx | High pressure cutout on the outdoor unit |
| 157.00 | Condensate float switch tripped: water backing up |
| 158 | Indoor coil frosting |
| 153 | Electric backup heat limit opened (the heat strips overheated) |
| 154 | Low airflow across the electric backup heat |
| 184.07 / 184.08 | Variable-speed protection lockout |
| 18 | Control fault on a piece of equipment |
| 92 | 24 volt fuse blown |
| 125 | Low 24 volt power |
Variable-speed AccuComfort outdoor units also report codes for refrigerant charge, the compressor drive and ground faults. Any of those is a call for a tech, and a ground fault means turn the unit off at its breaker first.
Older American Standard heat pumps
Older single-stage and two-stage outdoor units don’t talk to the thermostat. They have a light on the defrost or control board inside the service panel that blinks a count, and the meaning is printed on the panel’s wiring diagram. There’s high voltage in there with the power on, so leave that to a tech. The thermostat still tells you something’s wrong: the house stops warming up, or Aux runs nonstop.
How to reset an American Standard system
Set the thermostat to off. Turn off the breaker or the switch for the equipment, wait about five minutes, turn it back on and set the thermostat back. Do it once. For a heat pump, that means the outdoor unit’s breaker or the disconnect box beside it. Most thermostat alerts clear on their own once the problem goes away. Don’t restore factory defaults on the thermostat; that wipes the installer’s setup. If the same alert comes back, the history in Diagnostics is exactly what the tech needs to see.
Same codes as Trane
American Standard and Trane share their controls, so the Trane error code guide lists the same alerts, plus the board lights on variable-speed outdoor units. For furnace codes, see the American Standard furnace code guide. Common repairs and their usual range are on our American Standard repair page, and heat pump repair covers every brand.
The system we put in first
Built to take a beating. Put in by our crew.
Heat lamps, snow and rain on one outdoor unit: that’s Trane’s own film. We’re a Trane Comfort Specialist, on Trane’s own dealer locator, and when you pick a Trane, our crew puts it in.
Films: Trane’s own.
Book an American Standard repair
Call (703) 997-9757 or book online. A diagnostic visit is $99, and the tech reads the code, finds the part that set it and gives you the price before any work starts. We answer day or night. Our heating check is $67 per system, through December 31: furnace, heat pump or boiler. If someone already quoted you a new system, our free second opinion looks at it first. Rated 5.0 stars across 1,138 reviews on Google, Angi, Yelp, the BBB and Facebook, Virginia Class A license 2705192276.
Questions people ask
What does 126.00 mean on an American Standard thermostat?
A piece of equipment stopped communicating with the thermostat. Check the indoor and outdoor breakers and the outdoor disconnect and power cycle once. If it comes back, a wire or a board needs a technician.
Why is my American Standard heat pump on aux heat all the time?
The outdoor unit has probably stopped or can’t keep up. A 79 low pressure lockout, low refrigerant or a defrost problem are the usual causes. Check the thermostat’s alerts and call if the outdoor unit isn’t running.
What does error 79 mean on an American Standard heat pump?
The low pressure switch on the outdoor unit opened. Ice, a defrost problem, a dirty coil or a refrigerant leak can cause it. On the third trip it locks out until the power is cycled.
How do I clear an American Standard thermostat alert?
Most alerts clear on their own once the problem goes away. Turning the system’s breaker off for 20 to 30 seconds restarts everything. Don’t restore factory defaults; that erases the installer’s setup.
Are American Standard and Trane error codes the same?
Yes. Both brands are built by Trane Technologies and use the same communicating controls, so the alert numbers match, and their gas furnaces in the same model series show the same E codes.
What does 157.00 mean on an American Standard system?
The condensate float switch tripped because water is backing up in the drain pan or line. Check the pan and the condensate pump. If the pan keeps filling, the drain or the pump needs a technician.
